1. Field of the Invention
The present invention relates to a direct oxidation fuel cell.
2. Description of the Related Art
The direct oxidation fuel cell is directly supplied with a fuel in liquid phase and generates electrical energy by an electrochemical reaction of hydrogen contained in the fuel and air supplied separately.
The direct oxidation fuel cell may be of the passive type in which air is supplied at no-load independent of a pump or a blower, or an active type in which air is supplied by driving a pump or a blower.
The passive type direct oxidation fuel cell includes a membrane-electrode assembly (MEA) and anode and cathode plates disposed in close contact with respective sides of the MEA interposed therebetween.
The cathode plate includes a plurality of air vents through which air flows and is exposed to the atmosphere. The air vents have the same diameter and penetrate the cathode plate, and the diameter is of such a size that conductivity of the cathode plate can be sustained. In other words, the cathode plate is disposed in close contact with the MEA while maintaining a reference contact area such that a contact area closely contacting the MEA does not affect the conductivity.
However, the conventional passive type direct oxidation fuel cell generates water vapor through a reduction reaction of air in the MEA, and the cathode plate is exposed to the atmosphere, so that the water vapor contacts the atmosphere of a relatively low temperature and is condensed into water in the air vents of the cathode plate. The condensed water is collected in the air vents of the cathode plate, so that the condensed water blocks the air vents by operation of surface tension.
Accordingly, in the conventional direct oxidation fuel cell, the air vents of the cathode plate are blocked by the condensed water so as not to be properly supplied with air in the atmosphere. Therefore, efficiency and reliability of the entire fuel cell decreases.
In order to solve the aforementioned problem, the conventional direct oxidation fuel cell is constructed such that diameters of the entire air vents of the cathode plate increase. In this case, the contact area of the cathode plate with respect to the MEA becomes smaller than the reference contact area, so that electrons cannot properly move to the cathode plate.
Consequently, in the conventional direct oxidation fuel cell, the potential difference that occurs when electrons move decreases. Accordingly, the output efficiency of electrical energy decreases.